The process of manufacturing substrates for liquid crystal displays includes a number of steps in which glass sheets need to be supported and conveyed (transported) without damage to the sheet's major surfaces and, in particular, without damage to the sheet's “quality” surface upon which components of the display, e.g., thin film transistors and color filters, will be formed. For example, during the substrate manufacturing process, sheets need to be cut to size, edge ground, washed, and packaged and shipped or otherwise provided to the display manufacturer.
As sheet size has grown from a length of 1 meter to greater than 2 meters without a corresponding increase in sheet thickness, the lateral stiffness of the sheet has significantly decreased. At the same time, transport speed requirements have either remained constant or increased. Thus, the problem of transporting glass substrates for liquid crystal displays as it exists today can be described as trying to move a large glass sheet whose mechanical properties are not unlike those of tissue paper without touching the major surfaces of the sheet.
The glass sheets produced by the fusion process (see below) have extremely smooth surfaces. In practice, it has been found that a very smooth surface finish can sometimes be a contributing factor towards electrostatic discharge in the display manufacturing process. In such cases, it is has been found helpful to etch the surface of the sheet to reduce its smoothness. Only a light etch is needed to substantially reduce the probability of an electrostatic discharge. Accordingly, the etching can be performed without substantially impairing the ability of the glass sheet to transmit light. In addition to addressing the electrostatic discharge problem, an acid etch treatment can be also be useful in improving the bond between the metal films used in the LCD manufacturing process and the glass substrate.
In the past, it has been believed that etching of a major surface of a moving glass sheet required physical contact of the sheet with a roller. Specifically, it was believed that rollers were needed in order to achieve uniform etching. U.S. Patent Publication No. 2007/0271756 and JP 2004-203668 disclose such roller-based etching. Both of these references use rollers to apply an acid solution, even though they use water to support the glass sheet at other places in their overall processes.
As discussed and illustrated below, in accordance with the present disclosure, it has been surprisingly found that physical contact with the major surfaces of a moving glass sheet is not required for etching. In particular, it has been found that a highly uniform etch can be achieved during transport of large glass sheets without any physical contact with the major surfaces of the sheets. This is an important result since physical contact runs the risk of damaging and/or contaminating the surface of the glass.